Reconfigurable Devices using Liquid Crystal at Microwave Frequencies in Substrate Integrated Waveguide

[ES] La cantidad de servicios de telecomunicación se ha incrementado signiticativamente en las últimas décadas. El uso de teléfonos inteligentes, así como el Internet de las Cosas, está generando una saturación del espectro electromágnetico. Por tanto, los requisitos de los sistemas de microondas han cambiado para adaptarse a estos nuevos avances. Para satisfacer estas necesidades, se busca el desarrollo de dispositivos de bajo coste, volumen, peso y consumo. Además, interesa que sean espectralmente eficientes y fácilmente integrables con otros dispositivos. Entre todos los dispostivos de microondas, los filtros son elementos clave dentro de los sistemas de comunicaciones móviles e inalámbricas. Es por ello que el diseño de filtros que cumplan con los requisitos mencionados se ha convertido en un tema de gran interés. Para dar respuesta a este problema ha surgido la tecnología de Guía de Onda Integrada en Sustrato (Substrate Integrated Waveguide (SIW)), que permite la implementación de filtros con un reducido tamaño y fácilmente integrables con otros dispositivos en tecnología planar. Dicha tecnología presenta unas prestaciones en cuanto a manejo de potencia y pérdidas mejores que la tecnología de circuito impreso (Printed Circuit Board (PCB)), aunque no llegan a ser iguales que las de la guía de onda clásica. Por otro lado, la saturación espectral también lleva al estudio de filtros con respuestas variables en frecuencia, es decir, que puedan cambiar su frecuencia central y ancho de banda con el fin de adaptarse a las necesidades del sistema. Por ello, el objetivo general de esta Tesis es el análisis y diseño de nuevos filtros reconfigurables en tecnología integrada. El trabajo empieza con el estudio de los fundamentos de los filtros de microondas hasta llegar al diseño de resonadores reconfigurables en tecnología SIW usando el cristal líquido como material de reconfiguración. En primer lugar, se ha estudiado la influencia que los cambios en el valor de la permitividad dieléctrica en el interior de las estructuras filtrantes pueden tener en la respuesta de las mismos. En particular, se desarrollan filtros alternando secciones de línea con y sin dieléctrico dentro de una SIW vacía, Empty Substrate Integrated Waveguide (ESIW). Una vez hecho esto, se procede al estudio de materiales que tengan un valor de permitividad dieléctrica variable de alguna forma. En concreto, se ha realizado la caracterización de diferentes mezclas de cristal líquido a la frecuencia de microondas. Dicho material cambia su valor de permitividad cuando se le aplica un campo eléctrico o magnético. Dado que para la reconfiguración de la respuesta de los filtros se requiere de una estructura desacoplada en baja frecuencia, es decir, con más de un conductor, se ha desarrollado una estrategia para el desacoplo de la estructuras ESIW, la tecnología Decoupled Empty Substrate Integrated Waveguide (DESIW). Por último, se han diseñado resonadores en dicha tecnología DESIW, que se han llenado de cristal líquido y aplicado unos campos de polarización, consiguiendo variar su respuesta en frecuencia. Dichos resonadores constituyen el elemento básico para el desarrollo de filtros de microondas. Es por ello que el conocimiento obtenido en la Tesis es una buena base para futuros trabajos esta tecnología que permitan conseguir filtros de altas prestaciones.[CA] La quantitat de serveis de telecomunicació s'ha incrementat significativament en les últimes dècades. L'ús de telèfons intel$\cdot$ligents, així com la internet de les coses, està generant una saturació de l'espectre electromagnètic. Per tant, els requisits dels sistemes de microones han canviat per a adaptar-se a aquests nous avanços. Per a satisfer aquestes necessitats, se cerca el desenvolupament de dispositius de baix cost, volum, pes i consum. A més, interessa que siguen espectralment eficients i fàcilment integrables amb altres dispositius. Entre tots els dispositius de microones, els filtres són elements clau dins dels sistemes de comunicacions mòbils i sense fil. És per això que el disseny de filtres que complisquen els requisits esmentats s'ha convertit en un tema de gran interès. Per a donar resposta a aquest problema ha sorgit la tecnologia de Guia d'Ona Integrada en Substrat (Substrate Integrated Waveguide (SIW)), que permet la implementació de filtres amb una reduïda grandària i fàcilment integrables amb altres dispositius en tecnologia planar. Aquesta tecnologia presenta unes prestacions quant a maneig de potència i pèrdues millors que la tecnologia de circuit imprès (Printed Circuit Board (PCB)), encara que no arriben a ser iguals que les de la guia d'ona clàssica. D'altra banda, la saturació espectral també porta a l'estudi de filtres amb respostes variables en freqüència, és a dir, que puguen canviar la seua freqüència central i l'amplada de banda amb la finalitat d'adaptar-se a les necessitats del sistema. Per això, l'objectiu general d'aquesta tesi és l'anàlisi i el disseny de nous filtres reconfigurables en tecnologia integrada. El treball comença amb l'estudi dels fonaments dels filtres de microones, fins a arribar al disseny de ressonadors reconfigurables en tecnologia SIW usant el cristall líquid com a material de reconfiguració. En primer lloc, s'ha estudiat la influència que els canvis en el valor de la permitivitat dielèctrica a l'interior de les estructures filtrants poden tenir en la resposta d'aquestes. En particular, es desenvolupen filtres que alternen seccions de línia amb dielèctric i sense dins d'una SIW buida, Empty Substrate Integrated Waveguide (ESIW). Una vegada fet això, es procedeix a l'estudi de materials que tinguen un valor de permitivitat dielèctrica variable d'alguna forma. En concret, s'ha realitzat la caracterització de diferents mescles de cristall líquid a la freqüència de microones. Aquest material canvia el seu valor de permitivitat quan se li aplica un camp elèctric o magnètic. Atès que per a la reconfiguració de la resposta dels filtres es requereix una estructura desacoblada en baixa freqüència, és a dir, amb més d'un conductor, s'ha desenvolupat una estratègia per al desacoblament d'estructures ESIW, la tecnologia Decoupled Empty Substrate Integrated Waveguide (DESIW). Finalment, s'han dissenyat ressonadors en aquesta tecnologia DESIW, que s'han omplit de cristall líquid i aplicat uns camps de polarització, i s'ha aconseguit variar la seua resposta en freqüència. Aquests ressonadors constitueixen l'element bàsic per al desenvolupament de filtres de microones. És per això que el coneixement obtingut en la tesi és una bona base per a futurs treballs d'aquesta tecnologia que permeten aconseguir filtres d'altes prestacions.[EN] The number of telecommunication services has increased significantly in recent decades. The use of smartphones, as well as the Internet of Things, is generating a saturation of the electromagnetic spectrum. Therefore, the requirements of microwave systems have changed to adapt to these new developments and related challenges. For achieving these needs, the development of devices with low cost, volume, weight and power consumption is sought. In addition, it interests to be spectrally efficient, to offer high performance, and to be easily integrated with other devices. Among all microwave devices, filters are key elements within mobile and wireless communication systems. In this context, the design of filters that meet the aforementioned requirements has become a topic of great interest. For solving this problem, Substrate Integrated Waveguide (SIW) technology has emerged, which allows the implementation of filters with a small size and to be easily integrated with other devices in planar technology. This technology has better power handling and loss performance than Printed Circuit Board (PCB) technology, although they do not have the performance of the classic waveguide counterpart. On the other hand, the spectral saturation also leads to the study of filters with tunable frequency response, that is, they can change their central frequency and bandwidth, in order to fulfil the changing system requirements. Therefore, the general objective of this PhD Thesis work is the analysis and design of new reconfigurable filters in integrated technology. The work begins with the study of the basics of microwave filters until the design of reconfigurable resonators in SIW technology, using Liquid Crystal (LC) as reconfiguration material. Firstly, the influence that the change of the dielectric permittivity value inside the filtering structures have on the frequency response has been studied. Particularly, filters have been obtained by alternating line sections with and without dielectric material inside an empty SIW (Empty Substrate Integrated Waveguide (ESIW)). Once this is done, it is proceed to the study of materials that have a variable dielectric permittivity value. Specifically, the characterization of different LC mixtures at microwave frequencies has been carried out. This material changes its permittivity value when an electric or magnetic bias field is applied. A low-frequency decoupled structure is required for the reconfiguration of filters, that is, structures with more than one conductor. For that, a strategy for decoupling ESIW structures has been developed, i.e, the Decoupled Empty Substrate Integrated Waveguide (DESIW) technology. Finally, some resonators have been designed in DESIW technology, which have been filled with LC. The use of LC allows to tune their frequency response. These resonators are basic elements for the development of microwave filters. So that, the knowledge obtained in this Thesis work is a good basis for future works in this technology that allow for achieving high performance filters.Sánchez Marín, JR. (2019). Reconfigurable Devices using Liquid Crystal at Microwave Frequencies in Substrate Integrated Waveguide [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/132183TESI

A Microfluidic-Integrated SIW Lab-on-Substrate Sensor for Microliter Liquid Characterization

A novel microfluidic-integrated microwave sensor with potential application in microliter-volume biological/biomedical liquid sample characterization and quantification is presented in this paper. The sensor is designed based on the resonance method, providing the best sensing accuracy, and implemented by using a substrate-integrated-waveguide (SIW) structure combining with a rectangular slot antenna operating at 10 GHz. The device can perform accurate characterization of various liquid materials from very low to high loss, demonstrated by measurement of deionized (DI) water and methanol liquid mixtures. The measured relative permittivity, which is the real part of complex permittivity, ranges from 8.58 to 66.12, which is simply limited by the choice of test materials available in our laboratory, not any other technical considerations of the sensor. The fabricated sensor prototype requires a very small liquid volume of less than 7 µl, while still offering an overall accuracy of better than 3 %, as compared to the commercial and other published works. Key advantages of the proposed sensor are that it combines 1.) a very low-profile planar and miniaturized structure sensing microliter liquid volume; 2.) ease of design and fabrication, which makes it cost-effective to manufacture and 3.) noninvasive and contactless measurements. Moreover, since the microfluidic subsystem can potentially be detached from the SIW microwave sensor and, afterward, replaced by a new microfluidic component, the sensor can be reused with no life-cycle limitation and without degrading any figure of merit

Characterization of nematic liquid crystals at microwave frequencies

The use of nematic liquid crystal (LC) mixtures for microwave frequency applications presents a fundamental drawback: many of these mixtures have not been properly characterized at these frequencies, and researchers do not have an a priori clear idea of which behavior they can expect. This work is focused on developing a new procedure for the extraction of the main parameters of a nematic liquid crystal: dielectric permittivity and loss tangent at 11 GHz under different polarization voltages; splay elastic constant K11, which allows calculation of the threshold voltage (Vth); and rotational viscosity ¿11, which allows calculating the response time of any arbitrary device. These properties will be calculated by using a resonator-based method, which is implemented with a new topology of substrate integrated transmission line. The LC molecules should be rotated (polarized) by applying an electric field in order to extract the characteristic parameters; thus, the transmission line needs to have two conductors and low electric losses in order to preserve the integrity of the measurements. This method was applied to a well-known liquid crystal mixture (GT3-23002 from MERCK) obtaining the permittivity and loss tangent versus bias voltage curves, the splay elastic constant, and the rotational viscosity of the mixture. The results validate the viability of the proposed method

Transparent and Flexible Radio Frequency (RF) Structures

With increasing demand for a wearable devices, medical devices, RFID, and small devices, there is a growing interest in the field of transparent and flexible electronics. In order to realize optically transparent and flexible microwave components, novel materials can be used. The combination of new materials and radio frequency (RF) structures can open interesting perspectives for the implementation of cost effective wireless communication system and wearable device design. The transparent and flexible RF structures can facilitate its application in the transparent and curved surfaces. In this dissertation, we present several demonstrations, all based on optically transparent and flexible materials and structures. We firstly demonstrate an optically transparent, flexible, polarization-independent, and broadband microwave absorber. The bow-tie shaped array which possesses double resonances is designed and measured. The combined resonances lead to more than 90% total absorption covering a wide frequency range from 5.8 to 12.2 GHz. Due to the use of thin metal and PDMS, the whole structure is optically transparent and flexible. Secondly, we demonstrate a new method for fabricating transparent and stretchable radiofrequency small antennas by using stretchable micromesh structures. Size reduction is achieved by using the zeroth-order resonant (ZOR) property. The antennas consist of a series of tortuous micromesh structures, which provides a high degree of freedom for stretching when encapsulated in elastomeric polymers and is optically transparent. Accordingly, these antennas can be stretched up to 40% in size without breaking. The resonant frequency of the antennas is linearly reconfigurable from 2.94 GHz to 2.46 GHz upon stretching. Next, we describe an ultra-low profile and flexible triple-polarization antenna. It is realized by using ZOR array antenna with high port-to-port isolation. This flexible antenna is fabricated with a flexible substrate and silver nanowire vias to be used in various wearable applications. Lastly, we demonstrate a dual-band tri-polarized antenna based on half-mode hexagonal (HMH) SIW structure. CRLH HMHSIW antenna and ZOR HMHSIW antenna are designed to have dual-band operating frequencies. This novel antenna can provide much improved wireless communication efficiency for the WBAN system under various incident field angles and polarizations.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147562/1/tjang_1.pd

Analysis and Design of Low-Cost Waveguide Filters for Wireless Communications

The area of research of this thesis is built around advanced waveguide filter structures. Waveguide filters and the waveguide technology in general are renowned for high power capacity, low losses and excellent electromagnetic shielding. Waveguide filters are important components in fixed wireless communications as well as in satellite and radar systems. Furthermore, their advantages and utilization become even greater with increase in frequency, which is a trend in modern communication systems because upper frequency bands offer larger channel capacities. However, waveguide filters are relatively bulky and expensive. To comply with more and more demanding miniaturization and cost-cutting requirements, compactness and economical design represent some of the main contemporary focuses of interest. Approaches that are used to achieve this include use of planar inserts to build waveguide discontinuities, additive manufacturing and substrate integration. At the same time, waveguide filters still need to satisfy opposed stringent requirements like small insertion loss, high selectivity and multiband operation. Another difficulty that metal waveguide components face is integration with other circuitry, especially important when solid-state active devices are included. Thus, improvements of interconnections between waveguide and other transmission interfaces are addressed too. The thesis elaborates the following aspects of work: Further analysis and improved explanations regarding advanced waveguide filters with E-plane inserts developed by the Wireless Communications Research Group, using both cross coupled resonators and extracted pole sections (Experiments with higher filter orders, use of tuning screws, degrees of freedom in design, etc. Thorough performance comparison with competing filter technologies) - Proposing novel E-plane filter sections with I-shaped insets - Extension of the E-plane filtering structures with metal fins to new compact dual band filters with high frequency selectivity and miniaturized diplexers. - Introduction of easy-to-build waveguide filters with polymer insert frames and high-performance low-profile cavity filters, taking advantage of enhanced fabrication capabilities when using additive manufacturing - Developing new substrate integrated filters, as well as circuits used to transfer signals between different interfaces Namely, these are substrate integrated waveguide to metal waveguide planar transitions that do not require any modifications of the metal waveguides. Such novel transitions have been designed both for single and orthogonal signal polarizations

Wideband and UWB antennas for wireless applications. A comprehensive review

A comprehensive review concerning the geometry, the manufacturing technologies, the materials, and the numerical techniques, adopted for the analysis and design of wideband and ultrawideband (UWB) antennas for wireless applications, is presented. Planar, printed, dielectric, and wearable antennas, achievable on laminate (rigid and flexible), and textile dielectric substrates are taken into account. The performances of small, low-profile, and dielectric resonator antennas are illustrated paying particular attention to the application areas concerning portable devices (mobile phones, tablets, glasses, laptops, wearable computers, etc.) and radio base stations. This information provides a guidance to the selection of the different antenna geometries in terms of bandwidth, gain, field polarization, time-domain response, dimensions, and materials useful for their realization and integration in modern communication systems